1. Field of the Invention
The present invention relates to a liquid chromatograph such as a high-performance liquid chromatograph (HPLC) separating and analyzing various compounds within a sample.
2. Description of the Prior Art
FIG. 1 is a schematic channel block diagram showing a conventional HPLC, which is formed by a column 5 separating a sample, a pump part 1 feeding a mobile phase to the column 5, an auto injector 3 collecting the sample from a sampling needle 39 to a sampling loop 27 and introducing the collected sample into a mobile phase channel upstream the column 5 by switching a channel switching valve 29, a detection part 7 detecting the sample separated in the column 5 and a control part 41 controlling the operations of the pump part 1 and the auto injector 3.
The pump part 1 has a double plunger reciprocating feed pump 9. A suction side of a primary pump head 11 of the pump 9 is connected to a mobile phase container 15 storing the mobile phase through a check valve 13a, while a discharge side thereof is connected to a suction side of a secondary pump head 17 through a check valve 13b. A discharge side of the secondary pump head 17 is connected to the auto injector 3 through a drain valve 19 and a line filter 21. A pressure sensor 23 is provided on a channel between the secondary pump head 17 and the drain valve 19. The discharge side of the secondary pump head 17 can be switched and connected to the auto injector 3 or a drain by manually switching a lever 25 of the drain valve 19.
The auto injector 3 has a two-position six-port valve 29 switching and connecting a channel from the pump part 1 to the sampling loop 27 or the column 5. The sampling loop 27 is connected with the sampling needle 39 moving between an injection port 35 and a sample container 37 for sucking the sample from the sample container 37 and discharging the same in the injection port 35. The injection port 35 is connected to the column 5 by switching the valve 29. A measuring syringe 33 is connected to one port of the valve 29 through a three-way valve 31, to be connected to the sampling loop 27 by switching the valve 29.
The detection part 7 detecting the sample separated in the column 5 is connected downstream the column 5.
Channels between the injection port 35 and the valve 29, between the valve 29 and the column 5 and between the column 5 and the detection part 7 are formed by thin pipes for preventing the sample from dilution.
When filling up the overall channels with the mobile phase or substituting the mobile phase in this prior art, it takes remarkable time to substitute the mobile phase in the pump 9 having a relatively large volume if feeding the mobile phase at an ordinary low speed. However, if feeding the mobile phase at a high speed, pressure increases due to the thin pipes subsequent to the injection port 35 including the column 5. Therefore, the mobile phase cannot be fed to the channels subsequent to the injection port 35 at a high speed. In this regard, the pump 9 is driven at a high speed after switching the drain valve 19 to the drain side in the pump part 1 for introducing the mobile phase into the pump 9.
At this time, the lever 25 of the drain valve 19 is first manually moved to connect the discharge side of the secondary pump head 17 to the drain. Then, the pump 9 is driven at a high speed to discharge the mobile phase from the drain through the drain valve 19. After the primary and secondary pump heads 11 and 17 are filled up with a new mobile phase, the pump 9 is returned to an ordinary speed and the lever 25 of the drain valve 19 is manually switched to connect the discharge side of the secondary pump head 17 to the auto injector 3, thereby feeding the new mobile phase to the overall channels.
It is troublesome for an operator to manually open/close the drain valve 19 for substituting the mobile phase and automatization is awaited. However, in order to automatically open/close the drain valve 19, a high-torque motor is required since high pressure is applied to the drain valve 19, leading to a high cost for the apparatus.